[nhibernate-development] Illegal attempt to associate a collection with two open sessions

[senzacionale]

When i am inserting into DB everything works, but when i update i get
error of "Illegal attempt to associate a collection with two open
sessions". I use transaction, but if i do not have for example
userDao.CommitChanges(); nothing is stored to DB, but if i use
userDao.CommitChanges(); then i get previous error. I search in forum,
google try many things but no one works. Problem is that in VS 2008
update works, in IIS i get this problem.

Fluent NHibernate version:
1:0 RTM

Code for update

Code:
user.Name = txtName.Text;
user.Surname = txtSurname.Text;
user.HealthCardId = txtHealthCardId.Text;
user.Address = address;
userDao.Update(user);
userDao.CommitChanges();

Code:
public T Update(T entity)
        {
            NHibernateSession.Update(entity);
            return entity;
        }

Name and version of the database you are using:
MSSQL 2008

Full stack trace of any exception that occurs:

Quote:
Server Error in '/' Application.
Illegal attempt to associate a collection with two open sessions
Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.

Exception Details: NHibernate.HibernateException: Illegal attempt to
associate a collection with two open sessions

Source Error:

An unhandled exception was generated during the execution of the
current web request. Information regarding the origin and location of
the exception can be identified using the exception stack trace below.

Stack Trace:

[HibernateException: Illegal attempt to associate a collection with
two open sessions]
NHibernate.Collection.AbstractPersistentCollection.SetCurrentSession
(ISessionImplementor session) +237

NHibernate.Event.Default.OnUpdateVisitor.ProcessCollection(Object
collection, CollectionType type) +184
NHibernate.Event.Default.AbstractVisitor.ProcessValue(Int32 i, Object
[] values, IType[] types) +46
NHibernate.Event.Default.AbstractVisitor.ProcessEntityPropertyValues
(Object[] values, IType[] types) +74

NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.PerformUpdate
(SaveOrUpdateEvent event, Object entity, IEntityPersister persister)
+432
NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.PerformSaveOrUpdate
(SaveOrUpdateEvent event) +99

NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.OnSaveOrUpdate
(SaveOrUpdateEvent event) +333
NHibernate.Impl.SessionImpl.FireSaveOrUpdate(SaveOrUpdateEvent event)
+162
NHibernate.Impl.SessionImpl.SaveOrUpdate(String entityName, Object
obj) +151

NHibernate.Engine.SaveUpdateCascadingAction.Cascade(IEventSource
session, Object child, String entityName, Object anything, Boolean
isCascadeDeleteEnabled) +139
NHibernate.Engine.Cascade.CascadeOn(IEntityPersister persister, Object
parent, Object anything) +578

NHibernate.Event.Default.AbstractFlushingEventListener.CascadeOnFlush
(IEventSource session, IEntityPersister persister, Object key, Object
anything) +145
NHibernate.Event.Default.AbstractFlushingEventListener.PrepareEntityFlushes
(IEventSource session) +387

NHibernate.Event.Default.AbstractFlushingEventListener.FlushEverythingToExecutions
(FlushEvent event) +292
NHibernate.Event.Default.DefaultFlushEventListener.OnFlush(FlushEvent
event) +85
NHibernate.Impl.SessionImpl.Flush() +275

ProjectBase.Data.AbstractNHibernateDao`2.CommitChanges() in D:
\PROJEKTI
\eMedicine\ProjectBase.Data\AbstractNHibernateDao.cs:120
EMedicine.UserControls.UsersUC.btnAdd_Update(Object sender, EventArgs
e) in D:\PROJEKTI\eMedicine\eMedicine\UserControls\UsersUC.ascx.cs:390

System.Web.UI.WebControls.Button.OnClick(EventArgs e) +115
System.Web.UI.WebControls.Button.RaisePostBackEvent(String
eventArgument) +140
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler
sourceControl, String eventArgument) +29

System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
+2981

When i debug in IIS i get this

problem is in this code

Code:
public void CommitChanges() {
            if (NHibernateSessionManager.Instance.HasOpenTransactionOn
(SessionFactoryConfigPath)) {
                NHibernateSessionManager.Instance.CommitTransactionOn
(SessionFactoryConfigPath);
            }
            else {
                // If there's no transaction, just flush the changes
                NHibernateSessionManager.Instance.GetSessionFrom
(SessionFactoryConfigPath).Flush();
            }
        }

public void CommitTransactionOn(string sessionFactoryConfigPath) {
            ITransaction transaction = (ITransaction)
ContextTransactions[sessionFactoryConfigPath];

            try {
                if (HasOpenTransactionOn(sessionFactoryConfigPath)) {
                    transaction.Commit();
                    ContextTransactions.Remove
(sessionFactoryConfigPath);
                }
            }
            catch (HibernateException) {
                RollbackTransactionOn(sessionFactoryConfigPath);
                throw;
            }
        }

        public bool HasOpenTransactionOn(string
sessionFactoryConfigPath) {
            ITransaction transaction = (ITransaction)
ContextTransactions[sessionFactoryConfigPath];

            return transaction != null && !transaction.WasCommitted
&& !transaction.WasRolledBack;
        }

always is calling else statement in CommitChanges() method. When i
update never gone to commitchanges(). Any idea what can be wrong?